The present invention relates generally to vacuum pumps and more particularly to a rotary piston pump, having an expansion chamber with a gear and bearing chamber on one side of the expansion chamber and a bearing chamber on the other side, wherein the passages between the expansion chamber and the other chambers are separated by means of split seals.
In rotary piston pumps, two or more pistons rotate in an expansion chamber defined by a pump casing. The pistons rotate in opposite directions and perform a rolling movement relative to one another without mutual contact. The pistons also act to seal off the suction side from the outlet side of the pump along a line or surface. The movement of the pistons is effected by gears located in special gear chambers which are separated from the expansion chamber by means of partitions. These partitions between the expansion chamber and the gear chambers are provided with passages which receive shafts serving for the transmission of the rotary movement from the gears to the pistons. The gear chambers are filled with oil up to a certain level, the oil being supplied to shaft bearings and gear wheels, for example, by means of centrifugal disks.
Since a rotary piston pump is intended to operate without oil in the expansion chamber, oil and other lubricants must be prevented from penetrating into the expansion chamber from the gear chambers. Conversely, any substance present in the expansion chamber which could contaminate or destroy the lubricants in the gear chambers must be prevented from penetrating into the gear chambers. Therefore, it is necessary to ensure that the expansion chamber and the gear chambers are effectively separated at the passages receiving the shafts.
In order to achieve this separation, shaft seals are arranged in the bearing plates disposed between the rolling bearings and the passages leading into the expansion chamber. However, these seals have the disadvantage that they wear out very rapidly due to unavoidable friction. To avoid this disadvantage, it has been suggested to equip the passages receiving the shafts with split seals. These split seals do not provide an absolute sealing action, however, they are capable of preventing liquid particles from passing from one chamber into the other and, furthermore, they are not subject to wear.
Since, for manufacturing reasons, not every gap in the split seals is of the same size, pressure differences may occur which lead to compensating flows from one shaft passage to another, even when the initial pressure and the suction pressure remain constant. This effect occurs especially in multistage pumps where different pressures prevail at the various shaft passages. The above-mentioned compensating flows prevent the rotary piston pump from operating at maximum efficiency because they may force lubricant vapors from the gear chambers into the expansion chamber which should remain free of oil, and, similarly, they may force vapors from the expansion chamber into the gear chambers where the vapors may condense and contaminate or destroy the lubricants. Since the pressure compensation between the shaft passages takes place in part above the oil level in the gear chambers, spray oil may additionally be conveyed from the gear chambers into the expansion chamber and it would no longer be ensured that the expansion chamber is free of oil.
In order at least to reduce the amount of contaminating gases or vapors conducted from the gear chambers into the expansion chamber or vice versa, in accordance with a conventional method, the shaft openings are bled and evacuated individually by means of separate suction lines. This leads to high manufacturing costs, particularly of multistage pumps.
Another disadvantage of conventionally constructed pumps resides in that there is no possibility of checking for or removing undesirable substances occurring at the passages between the expansion chamber and the gear chambers. These substances may lead to failures of the pumps, particularly when such substances accumulate in large quantities.
An object of the present invention is to overcome the above and other disadvantages in rotary piston pumps, and to provide a pump capable of delivering oil-free gases and vapors by effectively separating the expansion chamber from the gear chambers.
Another object of the present invention is to provide a possibility for monitoring the operation of the pump.